Preparation of aromatic isocyanates

ABSTRACT

THE PROCESS FOR PREPARING AN ORGANIC ISOCYANATE BY REACTING AN ORGANIC NITRO COMPOUND WITH CARBON MONOXIDE IN THE PRESENCE OF A CATALYST SYSTEM COMPRISED OF A PALLADIUM COMPLEX OF A LEWIS BASE AND A UNIVALENT ANION. THE LEWIS BASE IS PREFERABLY A HETEROAROMATIC NITROGENCONTAINING COMPOUND CONTAINING BETWEEN FIVE AND SIX MEMBERS IN THE RING, CONTAINING NO ELEMENT OTHER THAN NITROGEN AND CARBON IN THE RING, CONTAINING NO MORE THAN TWO NITROGEN ATOMS IN THE RING, AND HAVING AT LEAST TWO DOUBLE BONDS IN THE RING SUCH AS PYRIDINE AND ISOQUINOLINE. THE UNIVALENT ANION IS PREFERABLY NCS-, N3-, NCO-, AND CN-. THE CATALYST SYSTEM MAY ALSO INCLUDE A SECOND COMPONENT SUCH AS MOLYBDENUM TRIOXIDE OR ANOTHER METAL OXIDE.

United States Patent O 3,585,231 PREPARATION OF AROMATIC ISOCYANATESThomas J. Hurley, Jr., Madison, and Martin A. Robinson, Orange, Conn.,assignors to Olin Mathieson Chemical Corporation No Drawing. Filed June21, 1968, Ser. No. 738,828 Int. Cl. B01j 11/84; C07c 119/04; C07d 31/40US. Cl. 260-453 15 Claims ABSTRACT OF THE DISCLOSURE The process forpreparing an organic isocyanate by reacting an organic nitro compoundwith carbon monoxide in the presence of a catalyst system comprised of apalladium complex of a Lewis base and a univalent anion. The Lewis baseis preferably a heteroaromatic nitrogencontaining compound containingbetween five and six members in the ring, containing no element otherthan nitrogen and carbon in the ring, containing no more than twonitrogen atoms in the ring, and having at least two double bonds in thering such as pyridine and isoquinoline. The univalent. anion ispreferably NCS, N 1 NCO-, and CN. The catalyst system may also include asecond component such as molybdenum trioxide or another metal oxide.

This invention relates to catalytic complexes useful in the preparationof organic isocyanates from organic nitro compounds.

Organic isocyanates are used extensively in the preparation of urethanefoams, coatings, and fibers, as well as in the preparation ofinsecticides, pesticides and the like. Commercial processes forpreparing organic isocyanates utilize the catalytic hydrogenation of anorganic nitro compound to form the corresponding amine, followed byreaction of the amine with phosgene to form the correspondingisocyanate. These processes are complex and expensive, and the need fora simplified, less expensive process is apparent.

In order to provide a simplified technique, it has been proposed toreact an organic nitro compound with carbon monoxide in the presence ofa catalyst. For example, British Pat. No. 1,025,436 discloses a processfor preparing isocyanates from the corresponding nitro compounds byreacting an organic nitro compound with carbon monoxide in the presenceof a noble metal-based catalyst. This process is not used commercially,because no more than trace amounts of organic isocyanates are formedwhen an organic nitro compound such as dinitrotoluene is reacted withcarbon monoxide using a noble metalbased catalyst, such as rhodiumtrichloride, palladium dichloride, iridium trichloride, osmiumtrichloride and the like.

Other proposed simplified techniques utilize other catalyst systems. Forexample, Belgian Pat. No. 672,405 entitled Process for the Preparationof Organic Isocyanates, describes the use of a catalyst system of anoble metal and/or a Lewis acid in the reaction between an organic nitrocompound with carbon monoxide.

Unfortunately, the yield of organic isocyanate afforded by thesesimplified techniques has not been significant enough to justify theiruse on a commercial scale.

It is a primary object of this invention to provide an improved processfor the preparation of organic isocyanates.

Another object of the invention is to provide a novel catalyst systemuseful in the direct conversion of organic nitro compounds to thecorresponding organic isocyanates.

Still a further object is to provide an improved proc- Patented June 15,1971 ess for preparing aromatic isocyanates such as phenyl isocyanate,toluene diisocyanates, and isocyanato-nitrotoluenes.

These and other objects of the invention will be apparent from thefollowing detailed description thereof.

It has now been discovered that the above-mentioned objects areaccomplished when an organic nitro compound is reacted -with carbonmonoxide at an elevated temperature and elevated pressure in thepresence of a catalyst system comprised of a complex of the formula: PdL A where L is a Lewis base and A is an univalent anion.

Certain metallic compounds promote the effectiveness of th catalystsystem, including oxides of metals of Groups V-B and VL-B of thePeriodic Table shown on page 122 of Inorganic Chemistry by Moeller, JohnWiley and Sons, Inc., 1952.

Any organic nitro compound capable of being converted to an organicisocyanate may be employed as a reactant. Generally, aromatic,cycloaliphatic, and aliphatic monoor polynitro compounds, which may besubstituted, if desired, can be reacted to form the corresponding monoorpoly-isocyanates by the novel proccess of this invention. The termorganic nitro compound, is used throughout the description and claims todefine unsbstituted as well as substituted organic nitro compounds ofthe type described herein. Typical examples of suitable organic nitrocompounds which can be reacted to form isocyanates include thefollowing:

(I) Aromatic nitro compounds (a) Nitrobenzene (b) Nitronaphthalenes (c)Nitroanthracenes (d) Nitrobiphenyls (e) Bis(nitrophenyl)methanes (f)Bis(nitrophenyl)ethers (g) Bis(nitrophenyl)thioether (h)Bis(nitrophenyl)sulfones (i) Nitrodiphenoxy alkanes (j)Nitrophenothiazines (II) Nitrocycloalkanes (a) Nitrocyclobutane (b)Nitrocyclopentane (c) Nitrocyclohexane (d) Dinitrocyclohexanes (e)Bis(nitrocyclohexyl)methanes (III) Nitroalkanes (a) Nitromethane (b)Nitroethane (c) Nitropropane (d) Nitrobutanes (e) Nitrohexanes (f)Nitrooctanes (g) Nitrooctadecanes (h) Dinitroethane (i) Dinitropropanes(j) Dinitrobutanes (k) Dinitrohexanes (l) Dinitrodecanes (m) Phenylnitromethane (n) Bromophenyl nitromethanes (o) Nitrophenyl nitromethanes(p) Methoxy phenyl nitromethanes (q) Bis-(nitromethyl)cyclohexanes (r)Bis-(nitromethyl)benzenes All of the aforementioned compounds may besubstituted with one or more additional substituents such as nitro,nitroalkyl, alkyl, alkenyl, alkoxy, aryloxy, halogen, alkylthio,arylthio, carboxyalkyl, cyano, isocyanate, and the like, and employed asreactants in the novel process 4 of this invention. Specific examples ofsuitable substi- (72) 1,4-dinitrocyclohexane tuted-organic nitrocompounds which can be used are as (73) Bis(p-nitrocyclohexyl)methanefollows:

(1) o-Nitrotoluene (2) m-Nitrotoluene (3) p-Nitrotoluene (4)o-Nitro-p-xylene (5) Z-methyl-l-nitronaphthalene (6) m-Dinitrobenzene(7) p-Dinitrobenzene (8) 2,4-dinitrotoluene (9) 2,6-dinitrotoluene (l0)Dinitromesitylene (11) 4,4'-dinitrobiphenyl (12) 2,4-dinitrobiphenyl(13) 4,4'-dinitrodibenzyl (14) Bis(p-nitrophenyl)methane (15)Bis(2,4-dinitrophenyl)methane 16) Bis(p-nitrophenyl)ether (17)Bis(2,4-dinitrophenyl) ether (18) Bis(p-nitrophenyl) thioether (19)Bis(p-nitrophenyl)sulfone (20) Bis(p-nitrophenoxy)ethane (21) a,x-Dinitro-p-xylene (22) 2,4,6-trinitrotoluene (23) 1,3,5-trinitrobenzene(24) l-chloro-2-nitrobenzene (25) 1-chloro-4-nitrobenzene (26)1-chloro-3-nitrobenzene (27) 2-chloro-6-nitrotoluene (28)4-chloro-3-nitrotoluene (29) l-chloro-2,4-dinitrobenzene (30)1,4-dichloro-2-nitrobenzene (31) Alpha-chloro-p-nitrotoluene (32)l,3,5-trichloro-2-nitrobenzene (33) 1,3,S-trichloro-2,4-dinitrobenzene(34) 1,2-dichloro-4-nitrobenzene 35) Alpha-chloro-m-nitrotoluene (36)1,2,4-trichloro-5-nitrobenzene (37) 1-bromo-4-nitrobenzene (3 8)l-bromo-2-nitrobenzene (39) 1-bromo-3-nitrobenzene (40)1-bromo-2,4-dinitrobenzene (41) a,u-Dibromo-p-nitrotoluene (42)a-Bromo-p-nitrotoluene (43) l-fiuoro-4-nitrobenzene (44)1-fluoro-2,4-dinitrobenzene (45) 1-fluoro-2-nitrobenzene (46)o-Nitrophenylisocyanate (47) m-Nitrophenyl isocyanate (48) p-Nitrophenylisocyanate (49) o-Nitroanisole (50) p-Nitroanisole (51) p-Nitrophenetole(52) o-Nitrophenetole (53) 2,4-dinitrophenetole (5 4 2,4-dinitroanisole(55) l-chloro-2,4-dimethoxy-5-nitrobenzene (56)1,4-dimethoxy-2-nitrobenzene (57) m-Nitrobenzaldehyde (58)p-Nitrobenzaldehyde (59) p-Nitrobenzoylchloride (60)m-Nitrobenzoylchloride (61) 3,5 -dinitrobenzoylchloride (62)Ethyl-p-nitrobenzoate 63) Methyl-o-nitrobenzoate (64)m-Nitrobenzenesulfonylchloride (65 p-Nitrobenzenesulfonylchloride (66)o-Nitrobenzenesulfonylchloride (67)4-chloro-3-nitrobenzenesulfonylchloride (68)2,4-dinitrobenzenesulfonylchloride (69) 3-nitrophthalic anhydride (70)p-Nitrobenzonitrile (71) m-Nitrobenzonitrile (74) l-nitro-n-hexane (75)2,2-dimethyl-l-nitrobutane (76) 1,6-dinitro-n-hexane (77)1,4-bis(nitromethyl)cyclohexane (78)3,3'-dimethoxy-4,4'-dinitro-biphenyl (79)3,3-dimethyl-4,4-dinitro-biphenyl In addition, isomers and mixtures ofthe aforesaid organic nitro compounds and substituted organic nitrocompounds may also be employed, as well as homologues and other relatedcompounds. Compounds which have both nitro and isocyanato substituents,such as 2-isocyanato-4-nitrotoluene, may also be employed as a reactant.

The process of this invention is particularly effective in theconversion of aromatic nitro compounds to organic isocyanates. As usedherein, the term aromatic nitro compounds represents those aromaticsnitro compounds having at least one nitro group attached directly to anaromatic hydrocarbon nucleus, such as benzene, naphthalene, and thelike, wherein the aromatic hydrocarbon nucleus may be substituted asillustrated above. Among the preferred organic nitro compounds which maybe used in the practice of this invention are the nitrobenzenes, bothmonoand polynitro, including isomeric mixtures thereof; thenitroalkylbenzenes, including the various nitrated toluenes and thenitrated xylenes; nitrated biphenyl and nitrated diphenylmethylene.Other preferred reactants include his (nitrophenoxy)alkylene andbis(nitrophenoxy)alkyl ethers. Generally, the organic nitro compoundsand substituted organic nitro compounds contain between 1 and about 20carbon atoms, and preferably between about 6 and about 14 carbon atoms.

Any Lewis base capable of forming a complex with palladium and aunivalent anion may be employed. The Lewis base used to prepare thecatalyst complex of this invention is preferably a heteroaromaticnitrogen compound containing between five and six members in the ring,containing only nitrogen and carbon in the ring, containing no more thantwo nitrogen atoms in the ring, and containing at least two double bondsin the ring. Suitable compounds of this type are disclosed in The RingIndex by Patterson and Capell, Second Edition, American ChemicalSociety, 1960, and Supplementals I, II and III. Derivatives of theheteroaromatic nitrogen compounds may also be utilized. The termderivatives when used In COIIJUDCUOI] with heteroaromatio compoundsthroughout the description and claims is intended to include addiilonsto the parent heteroaromatic ring of the following ype:

(I) Substituents on the ring (a) halides such as chlorine, bromine,iodine and fluorine (b) alkyl containing between 1 and 40 carbon atoms(c) aryl such as phenyl, cresyl and xylyl (d) olefinic such as allyl,vinyl (e) hydroxy (f) mercapto (g) amino (h) alkylamino (i) cyano (j)oximino (k) aldehyde thers such as aryl, alkyl, and alkenyl ethers (m)thioethers such as aryl, alkyl, and alkenyl ethers (n) carboxy (0)carbalkoxy (p) carbamyl (q) carboaryloxy (r) thiocarbamyl (II)Polycyclic analogues (a) fused benzene (b) fused cycloaliphatic (c)fused nitrogen-containing heteroaromatic (III) Simple salts (IV)Quaternary salts (V) Oxides (VI) Complexes with inorganic substancesother than noble metal halides (VII) Mixtures of two or more additionsof types I-VI 'Listed below are typical heteroaromatic nitrogencompounds and derivatives thereof which are suitable for use ascomponents of the catalyst complex of this invention.

( 1) Five membered ring containing one nitrogen (a) l-methyl pyrrole (b)l-phenyl pyrrole (2) Five membered ring containing two nitrogens (a)imidazole (b) l-methylimidazole (c) pyrazole (3) Fused benzene and fusednitrogen-containing heteroaromatic derivatives of five membered ringscontaining one nitrogen (a) indole (b) indolenine (3-pseudoindole) (c)2-isobenzazole (d) indolizine (e) 4aH-carbazole (f) carbazole (4) Sixmembered ring containing one nitrogen and derivatives thereof (a)pyridine (b) 2,6-dirnethylpyridine (c) 2,4,6-trimethylpyridine (d)4-phenylpyridine (e) 2-vinylpyridine (f) 2-styrylpyridine (g) 2bromopyridine (h) 'Z-chloropyridine (i) 3-chloropyridine (j)2,6-dichloropyridine (k) 2-bromo-4-methylpyridine (1) 2-fiuoropyridine(m) 2-allyloxypyridine (n) 4-phenylthiopyridine (o) Z-methoxypyridine(p) picolinic acid (q) nicotinic acid (r) 2,6-dicyanopyridine (s)pyridine-Z-aldeyde (picolinaldehyde) (t) Z-aminopyridine (u)4-dimethylaminopyridine (v) diphenyl-4-pyridylmethane (W)4-hydroxypyridine (x) Z-mercaptopyridine (y) 2-oximinopyridine(picolinaldoxime) (z) 4-tertiarybutylpyridine (5) Fused benzene andfused nitrogen-containing heteroaromatic derivatives of six memberedring containing one nitrogen (a) quinoline (b) 2-chloroquinoline (c)8-hydr oxyquinoline (d) isoquinoline (e) 'acridine (f) phenanthn'dine(g) 7,8-benzoquinoline (h) 4H-quinolizine (i) naphthyridine (j)car-boline (k) phenanthroline (l) benzo [h] isoquinoline =(m) benzo [g]quinoline (n) benzo [g] isoquinoline (o) benzo [h] quinoline (p) benzo[f] quinoline 6 (q) benzo [f] isoquinoline (r) 1H-benz0 [de] quinoline(s) 4H-benzo [de] quinoline (t) 4H-benzo [de] isoquinoline (u) 1H-benzo[de] isoquinoline (v) purine (w) adenine (x) pteridine (y) 7H-pyrazino[2,3-c] carbazole (z) pyrazino [2,3-d] pyridazine (aa) 4H-pyrido [2,3-c]carbazole (bb) Pyrido [1,2: 1,2 imidazo [4,5-b] quinoxaline (cc)6H-perimidine (dd) perimidine (6) Six membered ring containing twonitrogens and derivatives thereof (a) pyrazine (b)4,6-dimethylpyrimidine (c) 2,6-dimethylpyrazine (d) pyridazine (7) Fusedbenzene and fused nitrogen-containing heteroaromatic derivatives of sixmembered rings containing two nitrogens (a) quinoxaline (b)2,3-dimethylquinoxaline (c) phthalazine (d) quinazoline (e) phen'azine(f) cinnoline (8) Simple salts of heteroaromatic nitrogen compounds orderivatives thereof in sections 1-7 above (a) Simple salts inuludenitrates, hydrohalides, sulfates and acetates of these compounds such asthe following:

(1 pyridine hydrochloride (2) 2-chloropyridine-1-oxide hydrochloride 3)4-chloropyridine hydrochloride (4) 4,4-bipyridyl dihydrochloride (9)Quaternary salts of heteroaromatic nitrogen compounds or derivativesthereof of sections 2 and 47 above (a) Alkyl halides, where alkylcontains 1-40 carbon atoms, acyl halides, and nitroaryl halides, suchas:

(1) l-methylquinolinium chloride (2) laurylpyridinium chloride (3)1-(4-pyridyl) pyridinium chloride hydrochloride (10) Oxides ofheteroaromatic bases and derivatives thereof of sections 2 and 47 above(a) Oxides includes oxides of quinoline, pyridine, isoquinoline andimadazole, and are illustrated by the following oxides:

(l) pyridine-l-oxide (2) 4-bromopyridine-1-oxide (3)2-hydroxypyridine-l-oxide (4) picolinic acid-l-oxide (5 4-methoxypyridine-l-oxide (6) 2-bromo-6-methylpyridine-l-oxide (7)2-pico1ine-1-oxide (8) 4-picoline-l-oxide (l1) Complexes ofheteroaromatic nitrogen compound with inorganic substances (other thannoble metal halides) of sections 2 and 47 above (a) Complexes includepyridine, quinoline and isoquinoline complexes illustrated by thefollowing pyridine complexes:

(1) (PyfidlHe) 'F6Cl (2) pyridine-S0 (3) pyridine-CrO (4) pyridine-V01(5) pyridine-V 0 (6) pyridine-M00 As indicated above, heteroaromaticcompounds containing only nitrogen and carbon in the ring are preferablyused as the Lewis base, but a heteroaromatic compound which containsonly carbon and sulfur or only carbon and oxygen, or carbon and two ormore elements selected from the group consisting of nitrogen, sulfur,and oxygen may also be employed as the Lewis base. Typicalheteroaromatic compounds, in addition to those mentioned above, includethiophene, dibenzofuran, 2,5-diphenyloxazole, 2- mercaptobenzothiazole,thionaphthene, and the like, may also be used as the Lewis base.

The catalyst complex of this invention also contains a univalent anionother than a halide. The anion contains an element selected from thegroup consisting of nitrogen, oxygen, carbon, and tin. The preferredanions are those containing nitrogen. Typical univalent anions includeNCS, SCN, N NCO-, CN-, N N0 1 Cl0 SnCl and RCOO where R is alkylcontaining between 1 and about 8 carbon atoms, mixtures thereof and thelike.

Any convenient technique may be used to prepare the catalyst complex.For example, an alkali metal complex of palladium and univalent anion isreacted with an alcoholic solution of Lewis base to form the complexPdL- A where L and A are as defined above. This technique is describedin Inorganic Chemistry, vol. 3, No. 11, November 1964, page 1587. Inanother technique a complex of palladium, Lewis base, and halide isformed, and this complex is reacted with an alkali metal salt of thedesired univalent anion to yield the complex PdL A where L and A havethe same definitions presented above.

Although all of the aforesaid catalyst complexes have some effect onimproving the yield of isocyanate, certain complexes are significantlymore effective than others. Included in these more effective systems arethe following palladium complexes:

(1) Pd (pyridine) (SCN) (2) Pd (pyridine) (NO (3) Pd (pyridine) (NCO)The catalyst complex can be self-supported or deposited on a support orcarrier for dispersing the catalyst complex to increase its effectivesurface. Alumina, silica, carbon, barium sulfate, calcium carbonate,asbestos, bentonite, diatomaceuos earth, fullers earth, and analogousmaterials are useful as carriers for this purpose.

The reaction is carried out in the presence of a catalytic proportion ofthe catalyst complex. The proportion of catalyst complex is generallyequivalent to between about 0.001 and about 500 percent, and preferablybetween about 1 and about 100 percent by weight of the organic nitrocompound. However, greater or lesser proportions may be employed ifdesired.

The process of this invention operates effectively in the absence of asolvent, but improved overall yields of the organic isocyanates can beobtained when a solvent which is chemically inert to the components ofthe reaction system is employed. Suitable solvents include aliphatic,cycloaliphatic and aromatic solvents such as n-heptene, cyclohexane,benzene, toluene, and xylene, and halogenated aliphatic and aromatichydrocarbons such as dichloromethane, tetrachloroethane,trichlorofiuoroethane, monochloronapthalene, monochlorobenzene,dichlorobenzene, trichlorobenzene, and perchloroethylene, as well assulfur dioxide, mixtures thereof and the like.

The proportion of solvent is not critical and any proportion may beemployed which will not require excessively large equipment to contain.Generally the weight percent of organic nitro compound in the solvent isin the range between about 2.0 and about 75 percent, but greater orlesser proportions may be employed if desired.

The order of mixing the reactants is not critical and may be variedwithin the limitations of the equipment employed. In one embodiment, theorganic nitro compound, catalyst complex, and if desired, solvent, ischarged to a suitable pressure vessel such as an autoclave which waspreviously purged with nitrogen, and which is preferably provided withagitation means such as a stirrer or an external rocking mechanism. Atstart-up, carbon monoxide is fed into the autoclave until a pressure isattained, at ambient temperature which is generally between about 30 andabout 10,000 p.s.i.g. After the reaction proceeds and heat is applied,the pressure may increase to as high as 30,000 p.s.i.g. The preferredreaction pressure is between about and about 20,000 p.s.i.g. However,greater or lesser pressures may be employed if desired.

Generally the quantity of carbon monoxide in the free space of thereactor is suflicient to maintain the desired pressure as well asprovide reactant for the process, as the reaction progresses. Ifdesired, additional carbon monoxide can be fed to the reactor eitherintermittently or continuously as the reaction progresses. The reactionis believed to progress in accordance with the following equation:

where R is the organic moiety of the organic nitro compound reactant ofthe type defined above, and n is the number of nitro groups in theorganic nitro compound. The total amount of carbon monoxide added duringthe reaction is generally between about 3 and about 50 and preferablybetween about 8 and about 15 moles of carbon monoxide per nitro group inthe organic nitro compound. Greater or lesser amounts may be employed ifdesired. The highest carbon monoxide requirements are generally utilizedin a process in which the carbon monox ide is added continuously, butsuitable recycle of the carbon monoxide containing gas streams greatlyreduces the overall consumption of carbon monoxide.

The reaction temperature is generally maintained above about 25 C. andpreferably between about 100 and about 250 C. Interior and/or exteriorheating and cooling means may be employed to maintain the temperaturewithin the reactor within the desired range.

The reaction time is dependent upon the organic nitro compound beingreacted, temperature, pressure, and on the amount of catalyst beingcharged, as well as the type of equipment being employed. Usuallybetween one-half hour and 20 hours are required to obtain the desireddegree of reaction, in a batch technique, but shorter or longer reactiontimes may be employed. In a continuous process, the reaction may be muchfaster, i.e. substantially instantaneous, and residence time may besubstantially less than batch reaction.

The reaction can be carried out batchwise, semi-continuously orcontinuously.

After the reaction is completed, the temperature of the crude reactionmixture may be dropped to ambient temperature, the pressure vessel isvented, and the react on products are removed from the reaction vessel.Filtrat1on or other suitable solid-liquid separation techniques may beemployed to separate the catalyst from the reaction product, andfractional distillation is preferably employed to isolate the organicisocyanate from the reaction product. However, other suitable separationtechniques such as extraction, sublimation, etc., may be employed toseparate the organic isocyanate from the unreacted organic nitrocompound and any by-products that may be formed.

Organic isocyanates produced in accordance with the technique of thisinvention are suitable for use in preparing polyurethane compositionssuch as foams, coatings, fibers, and the like by reacting the organicisocyanate with a suitable polyether polyol in the presence of acatalyst and, if desired, a foaming agent. In addition, the organicisocyanates may be used in the preparation of biologically activecompounds.

Some improvement in the conversion and yield of organic isocyanates canbe obtained by employing a cata lyst system which not only contains apalladium complex of the type described above, but also contains asecond component comprised of certain metal oxides. Oxides suitable as asecond component of the catalyst system include at least one oxide of anelement selected from the group consisting of vanadium, molybdenum,tungsten, niobium, chromium and tantalum, as described in copendingUnited States patent application Ser. No. 619,158, filed Feb. 28, 1967,for Process, by Wilhelm J. Schnable, Ehrenfried H. Kober and Theodore C.Kraus. These elements are found in Groups V-A and VI-A of the PeriodicTable. Suitable oxides of this type include chromic oxide (Cr O chromiumdioxide (CrO); molybdenum sesquioxide (M 0 molybdenum dioxide (M00 andmolybdenum trioxide (M00 niobium monoxide (NbO), niobium oxide (NbO andniobium pentoxide (Nb O tantalum dioxide (Ta O tantalum tetraoxide (Ta Oand tantalum pentoxide (Ta O tungstic oxide (W0 and tungstic trioxide(W0 vanadium dioxide (V 0 vanadium trioxide (V 0 vanadium tetraoxide (V0 and vanadium pentoxide (V 0 Mixtures of two or more of these oxidesmay be employed as one component of the catalyst mixture. The proportionof the second component of the catalyst system, when one is employed, isgenerally equivalent to a weight ratio of the Group V-A or VI-A metalcompound to the palladium complex in the catalyst system generally inthe range between about 0.000111 and about 25: 1, and preferably in therange between about 0.005:1 and about 5:1.

The following examples are presented to describe the invention morefully without any intention of being limited thereby. All parts andpercentages are by weight unless otherwise specified.

EXAMPLE 1 The reactor employed in these examples was a 100 ml.stainless-steel autoclave (316 grade) adapted to be rocked in a rockerat a rate of about 36 cycles per minute. The reactor was provided with aglass liner, heating coils and means for feeding gas into the gas spaceto obtain the desired pressure.

A palladium complex Pd(pyridine) (NCS) (0.6 gram), 3.0 gramsm-dinitrotoluene and 5 ml. of ortho dichlorobenzene were charged to thereactor, and the reactor was sealed. Carbon monoxide was fed to thereactor until a pressure of 5000 p.s.i.g. was obtained. The reactor washeated to 'a temperature of 190 C. for a period of 1.5 hours, withconstant rocking during the reaction. At the end of this period, carbonmonoxide was released from the autoclave, the temperature was allowed todrop to ambient temperature, the reaction was removed from the autoclaveand filtered. The liquid product as analyzed by vapor phasechromotography showed a conversion of 54 percent of the dinitrotoluenereactant, and a yield of 35 percent of the product asisocyanate-containing compounds.

EXAMPLES 2-5 The procedure of these examples, employing the apparatus ofExample 1 was repeated with the exception that the palladium complex wasreplaced with a catalyst listed below in the table in the proportionrecited therein.

9--Dinitrobis(isoquinoline)palladium (II) l0Diisocyanatobis(isoquinoline)palladium (II) 1 1-Dicyanobis(isoquinoline) palladium (H)12Diisothiocyanatobis(quinoline)palladium (II)13Dinitratobis(quinoline)palladium (II)14-Dinitrobis(quinoline)palladium (II)15-Diisocyanatobis(quinoline)palladium (I'I)-l6-Dicyanobis(quinoline)palladium (I l) Significant conversions ofdinitrotoluene, nitrobenzene, or mononitro-monoisocyanato-toluene to thecorresponding isocyanates were obtained when each of the above complexeswere employed.

EXAMPLE 17 The procedure of Example 1 was repeated with the exceptionthat the palladium complex was Pd(isoquinoline) (SCN) in the amount of0.9 gram. The liquid product was analyzed by vapor phase chromatographyand showed a conversion of 18 percent of the dinitrotolulene reactant,and a yield of 67 percent of the product as toluene diisocyanate.

Various modifications of the invention, some of which have been referredto above, may be employed without departing from the spirit of theinvention.

What is desired to be secured by Letters Patent is:

1. In the process for preparing an aromatic isocyanate by reacting anaromatic nitro compound with carbon monoxide at an elevated temperatureand an elevated pressure in the presence of a catalyst, the improvementwhich comprises employing as said catalyst, a palladium complex havingthe formula PdL A A. where L is (1) a heteroaromatic compound containing(a) between 5 and 6 members in the ring, (b) only nitrogen and carbon inthe ring, (c) no more than two nitrogen atoms in the ring, and (d) atleast two double bonds in the ring, and

a (2) derivative of A(1), and B. where A is a univalent anion containingnitrogen selected from the group consisting of (1) NCS" (2) SCN- (4) NCO2. The process of claim 1 wherein said heteroaromatic compound isselected from the group consiting of pyridine, isoquinoline, andquinoline.

3. The process of claim 2 wherein said univalent anion l S NO2 4. Theprocess of claim 2 wherein said univalent anion is N03 5. The process ofclaim 2 wherein said univalent anion is NCS Proportions Percent yield ofcatalyst,

percent by Pressure, React on Percent Toluene Total Ex. Catalyst weightp.s.i.g. Temp., 0. time, mm. conversion dnsocyanate isoeyanate 2Dinitratobis(pyridine)Pal1adiu m (II) 20 2, 530 250 150 99 5 14 3 2 do20 2, 490 250 150 99 10 10 4 Dinitrobis(pyridine)palladium (II) 6 2,550190 90 34 0 18 5 Diisocyanatobis(pyridlne)palladium (II) 20 6,000 190900 98 2 16 1 Catalyst system also contains 6.67% of cupric bromide.

2 Catalyst system also contains 6.67% of cupric bromide and 0.33% ofmolybdenum trioxide.

The procedure and apparatus of Example 1 was repeated with the exceptionthat the palladium complex was replaced with the following palladiumcomplexes.

Examples:

6Dicyanobis(pyridine)palladium (I l) 7-Diisothiocyanatobis(isoquinoline)palladium (II) S-Dinitratobis(isoquinoline) palladium (II)10. The process of claim 2 wherein said palladium complex isPd(pyridine) (SCN) 11. The process of claim 2 wherein said palladiumcomplex is Pd(pyridine) (NO 12. The process of claim 2 wherein saidpalladium complex is Pd(pyridine) (NCO) 13. The process of claim 2wherein the proportion of said catalyst is between about 0.001 and about500 weight percent of said organic nitro compound.

14. The process of claim 13 wherein the proportion of 10 said catalystsystem is between about 1 and about 100 weight percent of said organicnitro compound.

15. The process of claim 14 wherein said aromatic nitro compound isselected from the group consisting of nitrobenzene, dinitrotoluene,nitroisocyanatotoluene, and 15 mixtures thereof.

1 2 References Cited UNITED STATES PATENTS 10/1968 Stern et al 2604538/1969 Hardy et a1 260-453 US. Cl. X.R.

